Can Not Perform Calibration Of The Governor Actuator With The "PDT" Or With A Laptop And M300 Technician Or Engine Constantly Runs At Low Idle Caterpillar

Problem:

Field complaints report the "position feedback signal" from the governor actuator back to the external electronic controller is interrupted. An explanation is that either the red wire, brown wire, or the black wire, or all three wires are broken and do not allow the correct information (position feedback) to reach the electronic controller.

If the Portable Diagnostic Tool (PDT) in "PROC" function or the M300 Technician is used in "status" menu, the following values can be verified when moving the speed dial position from low idle to high idle:

- Speed Dial Position...still varies from 0 to 255 bits

- Gov Actuator Request...still varies from a lower value to a higher value (don't forget to turn off the AEC function and Heavy lift function)

BUT

- Gov Actuator Position...remains constant at 255 bits (whatever the position of the speed dial).

The result is that because of the wrong feedback signal, the controller believes the actuator is at high idle. The electronic controller is trying to correct the situation by reducing the speed dial request and keeps the engine at low idle.

Two other consequences of this wrong feedback are that the "rpm difference" shows a value of "-1000" rpm's (example) and that the calibration of the actuator can not be accomplished and interrupts with the error message "feedback too high"

Solution:

If this condition exists, make a further check that the "Gov Actuator Position" also remains constant at 255 bits when the governor actuator cylinder is pushed in manually. Use a pry bar to move the cylinder. This condition will prove that the feedback wires are interrupted.

Disconnect the "Deutsch connector" at the back of the governor actuator. This is located at the source of feedback signal (bottom) and not at the actuator solenoid (top harness).

Illustration 1.

Governor Actuator

(1) Actuator Solenoid.

(2) Wiring harness in question.

(3) Deutsch connector.

(A) Location of suspected broken wires.

Use a Multimeter to measure the internal resistance of the governor position sensor. The resistance values should be about 35 Ohm between the BK and the RD wire, about 35 Ohm between the BK and the BR wire, and about 70 Ohm between the RD wire and the BR wire.

If you find an open circuit in one or more of these connections, this is the source of the problem. If no open is discovered at first, move or shake the wires and check if this is not an intermittent problem. There may be a bad contact.

When the problem is confirmed, Caterpillar recommends that you install a new 112-7593 Governor Actuator and calibrate it.

NOTE: If a new governor actuator is not available, it is still possible to repair the connections for the position feedback sensor. Follow this procedure:

1. Release the hydraulic pressure.

2. Disconnect the hoses from the governor actuator.

3. Remove the governor from the bracket.

4. Open the front of the cylinder to remove the spring.

5. Open the back plug at the feedback port to gain access to the Allen bolt of the sensor and unscrew the bolt.

6. Test all three wires for continuity between the sensor connection and the Deutsch connector until you find the interrupted wire that needs to be repaired.

7. After installing the governor actuator, carefully mount the wiring with the use of straps as shown in Illustration 2. Illustration 2.

Illustration 2.

(B) Mount wires from actuator solenoid and rest of harness to actuator.

(C) Strap all wires in one bundle.

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